1. Field of the Invention
This invention relates to photosensitive compositions useful for photomechanical processes and photosensitive copying processes, and more particularly to photosensitive compositions comprising a novel photosensitive resin prepared by condensing a specific alkali-soluble co-condensated novolak resin (hereinafter referred to as "co-condensated novolak resin") with a o-quinonediazido compound and to photosensitive compositions comprising the co-condensated novolak resin and a photosensitive o-quinonediazido compound admixed therewith.
2. Description of the Prior Art
It is widely known that o-benzoquinonediazido compounds and o-naphthoquinonediazido compounds are useful as photosensitive substances for photomechanical and photosensitive copying processes. These o-quinonediazido compounds are usable also in the form of sulfonic acids and carboxylic acids. Similarly useful as photosensitive materials are sulfonic acid esters and carboxylic acid esters of these o-quinonediazido compounds and various hydroxy-containing compounds, and amide compounds prepared from such diazido compounds and various amines.
The above-mentioned o-quinonediazido compounds have the characteristics that when exposed to light, the compounds decompose to form free carboxyl groups, such that when a coating of such compounds is exposed to light and then treated with an aqueous alkali solution such as a solution of sodium tertiary phosphate, the exposed portion dissolves away to give an image area.
However, when used singly as photosensitive materials, such compounds separate out in the form of crystals, are unable to form satisfactory coatings and afford image areas of low mechanical strength. Accordingly it is also known to use o-quinonediazido compounds as admixed with alkali-soluble resins, such as phenol novolak resin, in such manner that the alkali resistance of the nonexposed portion is utilized to prevent the alkali-soluble resin from dissolving in an alkali solution and thereby form images. This method is often used for economical reasons.
Especially for applications in which the image formed on a metal base material is subjected to etching or the image formed on a printing plate is used as it is, it is critical to use an alkali-soluble resin of excellent properties as a support for the o-quinonediazido compounds, whereby the photosensitive layer can be prevented from crystallization to afford an image of improved mechanical strength. For the same purpose, U.S. Pat. No. 3,046,120 discloses a polymer prepared by the condensation of o-benzoquinonediazido sulfonylchloride or o-naphthoquinonediazo sulfonylchloride with an alkali-soluble phenol-formaldehyde resin of the novolak type, or o- or m-cresol-formaldehyde resin. The disclosed compound nevertheless still fails to give images of desired strength since the image area is liable to dissolve away in an aqueous alkali solution and is low in adhesiveness to the base material. Moreover the image area is poor in fat sensitivity.
The object of the present invention is to overcome the drawbacks of the conventional photosensitive compositions of the type described and to provide photosensitive compositions which afford photosensitive materials retaining high resistance to aqueous alkali solutions over the unexposed area when exposed to light and printing plate materials having high fat sensitivity and which can be stored over a prolonged period of time without undergoing noticeable changes in photosensitivity and developing properties.